In recent years, various types of electronic apparatuses such as a notebook type personal computer and tablet have been developed. Most of such electronic apparatuses have a port such as a Universal Serial Bus (USB) port to which a portable device can be attached. This USB port not only allows communication between the electronic apparatus and the portable device but also can be used to charge the portable device or to supply power to it.
To charge the portable device at high speed, it is necessary to enable the portable device to draw a high current from the USB port, that is, to enable to supply a relatively high current from the USB port to the portable device.
If, however, the portable device is always allowed to draw a high current from the USB port, the electronic apparatus itself may not normally operate due to a power shortage.